Japanese Laid-Open Patent Publication No. 2003-260536 describes a silent chain composed of interleaved, toothed, link plates and connecting pins, in which sprocket tooth-engaging surfaces of inner flanks and outer flanks of the link plate teeth are formed by shaving to reduce wear of sprocket teeth surfaces and to prevent flexion failure.
The surfaces of the link plates are remarkably improved by shaving. However, in a direct injection engine, combustion residues such as carbon and similarly abrasive substances, generally referred to as “soot,” are generated by incomplete combustion of fuel such as diesel fuel. When the shave surfaces of the chain are exposed to this soot, especially when the soot, along with engine lubricating oil, enters the connecting pin holes in the link plates, the soot promotes wear between the inner surfaces of the pin holes and the outer surfaces of the pins. The wear of the pin holes, and of the pins, results in “wear elongation” of the chain over time. Wear elongation, in turn, impairs engine performance, and brings about the need for early timing chain replacement.
The soot in a direct injection engine can also adhere to sprocket tooth-engaging surfaces of the link plates and to the backs of the link plates, causing wear of the sprocket teeth, and link plate teeth as well as wear of chain guide shoes and tensioner lever shoes on which the backs of the link plates slide. Excessive wear of these components significantly shortens their useful life.
This invention addresses the above-mentioned problems. In particular, objects of the invention include one or more of the following objects: reduction of pin hole wear, reduction of wear elongation; reduction in sprocket tooth wear, reduction in link plate tooth wear, reduction of guide shoe and tensioner shoe wear, and improvement of link plate fatigue resistance. The advantages of the invention are especially significant in the case in which the chain is utilized as a timing chain in a direct injection internal combustion engine.